Within 6 months after the initial occurrence of hepatocellular carcinoma, if the diameter is < 2cm, it is diagnosed as "small hepatocellular carcinoma", the cancer cells have not spread yet, and can be cured by removing or destroying the cancer nodules (ablation); most of the carcinomas > 2cm are found more than 6 months later, and will grow exponentially soon, and may grow into a huge mass in a year. The cancer cells will enter the blood vessels from the original location to form small cancer emboli, which will spread from near to far and grow into multiple daughter cancers, and even metastasize to the outside of liver (common lung and bone marrow), which is difficult to remove and insensitive to chemotherapy, with serious consequences. Alpha-fetoprotein (AFP) is a very important serum marker of liver cancer and must be checked regularly every 6 months for patients who may develop liver cancer. However, AFP is not “definitely elevated in liver cancer”. About a quarter of patients with liver cancer (even massive liver cancer) have normal fetoprotein, so ultrasound must be performed at the same time. Ultrasound alone also often misses the test, and most of the ultrasound findings are only sclerotic nodules or even false images, so they must be checked at the same time as the methemoglobin. Combined examination of fetoprotein and ultrasound every 6 months is a commonly recommended screening program for liver cancer at home and abroad. The current dramatic increase in survival rate of liver cancer is not mainly due to the advancement of treatment, but due to the detection of small curable liver cancers by this screening program. In patients with cirrhosis or even hepatitis with obvious fibrosis, methemoglobin can be mildly to moderately elevated; in some acute active patients, transaminases rise by hundreds of U/L and methemoglobin also increases by hundreds of ng/ml, but as long as one or two months of entecavir or tenofovir is taken, methemoglobin can be ruled out as the virus and transaminase levels drop! On the contrary, methemoglobin continues to rise, even if it is not detected by CT or MRI, do not relax, it may be that the cancer nodules are smaller than the limit of possible detection by imaging (<< span="">0.5cm), and follow-up examination can detect the smallest liver cancer, which can get the most complete eradication at the best time.